Trapped Neutrophil Syndrome (TNS)

(Also referred to as Hereditary Neutropenia)

TNS is an inherited fatal immune disorder found in Border Collies. Although thought to have been around for a long time it is only recently that scientists have started to get a greater understanding of the way it actually works, it’s affects on the animal and means of inheritance.

Neutrophils are the precursors to white blood cells, produced in the bone marrow, and in a normal animal, released into the blood to fight infections. In a TNS affected animal these Neutrophils cannot be released from the bone marrow so the animal is unable to mount an effective immune response to infection.

Symptoms can fluctuate greatly, depending on which infections the pup happens to contract; it is because of this that the disease has been difficult to recognise in the past. There are still very few vets in the UK aware of this condition. Symptoms can be seen from as early as 2 weeks old. Affected pups are typically smaller than their siblings with slower growth rates and often appear to have a weedy head and poorly conditioned coat. Other symptoms include vomiting and diarrhoea, in appetence, high temperatures/fever, swollen and painful joints and lameness.

Onset of symptoms frequently coincides with the animal’s first vaccination, since this is often the first challenge to a pups’ immune system. Live vaccines are designed to mimic certain infections so that the pups’ immune system can produce antibodies against it and recognise it, should it encounter the infection again in the future. In a TNS affected pup of course this does not happen and the puppy will quickly develop the infection. It is vital therefore that if a puppy is suspected of having the disease it does not receive any form of vaccination.

Up until recently diagnosis was difficult and involved invasive techniques. A pup displaying the clinical symptoms described above will usually be blood tested. A low Neutrophil count would point to TNS but it is not conclusive since other factors such as viral or bacterial infections may also cause this. A bone marrow biopsy is the best way to detect the disease, if the Neutrophil levels in the bone marrow are higher than those in the blood it is a sign that these are trapped hence ‘Trapped Neutrophil Syndrome’.

Recently a chromosome marker test has become available for this disease; this test is able to detect the chromosome carrying TNS in affected and carrier animals so it is now possible to obtain a diagnosis without using the invasive bone marrow biopsy technique. Research has shown that the mode of inheritance is recessive, so both parents must carry the gene to produce an affected pup. Initially the marker test was only useful in suspected cases and close relatives of known affected/carrier animals. Recent research and results have shown that the test is also reliable in those dogs that are not related to known affected/carriers. While many at first thought the disease might be limited to the Australasian bloodlines, carriers have been identified in all British and ISDS bred dogs too. The test is now available for all Border Collies so all breeding stock can now be tested and therefore eradicate this disease from the gene pool.